1. Technical Field
The present invention relates to a technique of measuring the profile of a surface of a measuring target. The present invention also relates to a technique of measuring or observing the surface of the measuring target.
2. Related Art
A technique of using color information and a technique of using luminance information are conventionally known as a technique of measuring a normal profile of a measuring target.
A color highlight method is known as a technique of measuring the normal profile using the color information. As shown in FIGS. 20A and 20B, the color highlight method includes arranging red, blue, and green ring lightings in a dome, and irradiating the measuring target with each color. The direction of a normal line (only zenith angle component) of the surface to be measured is distinguished in three ways by analyzing the color of reflected light from the measuring target to calculate the surface profile. As a modification of the color highlight method, a technique (refer to, for example, Japanese Patent Application Laid-Open No. 3-142303) of finely measuring the normal line (only zenith angle component) of the surface to be measured by arranging great number of concentric lightings in a hood, and a technique (refer to, for example, Japanese Patent Publication No. 3553652) of performing photography using two types of lighting patterns of a zenith angle component measurement pattern and an azimuth angle component measurement pattern, and calculating the zenith angle component and the azimuth angle component of the normal line from the respective images are known.
An illuminance difference stereo method is known as a technique of measuring the normal profile to be measured using the luminance information. As shown in FIG. 21, the illuminance difference stereo method is a method of acquiring the normal direction at each point of the object surface based on a plurality of images photographed one at a time under three or more different light sources using shadow information of the object. More specifically, the luminance information is acquired using an object which profile is known, for example, from three images photographed under different light sources. The direction of the normal line is uniquely determined by a set of luminance values, and is saved as a table. In time of measurement, photography is performed under three light sources, and the normal line is obtained from a set of luminance information with reference to the created table. According to the illuminance difference stereo method, the normal line of an object, which does not have a perfect mirror surface, can be obtained.